Obstetrics and Gynecology - A.M. Hromova 2000

Multiple pregnancy
General provisions

A Multiple Pregnancy is defined as a condition in which two or more fetuses develop simultaneously within the mother's body, and the resulting delivery is referred to as a multiple birth.

The incidence of twins ranges from 0.4 to 1.6%. The frequency of twin pregnancies is approximately 1:80, triplets - 1:80², and quadruplets - 1:80³. Among newborns, male twins predominate.

The exact causes of multiple pregnancies are not fully understood. Heredity plays a certain role. Frequent causes of multiples include The Use of ovulation-inducing drugs, assisted reproductive technology (In vitro Fertilization), and the discontinuation of oral contraceptives. Uterine developmental anomalies (such as a bicornuate Uterus or a uterine septum), which can lead to the simultaneous maturation of two or more eggs in the Ovaries, are also significant. Contributing factors include the fertilization of "aged" eggs (24 hours or more after ovulation), maternal age over 35, exposure to toxic substances, Hypoxia, cold stress, and ultraviolet irradiation.

Multiple pregnancy can result from the fertilization of two or more eggs that have matured simultaneously (polyovulation), or from The Development of multiple embryos from a single fertilized egg (polyembryony).

THE ORIGIN OF dizygotic or multizygotic twins may be due to:

a) simultaneous ovulation followed by the fertilization of two or more eggs that matured in different follicles of the same Ovary (ovulatio uniovularis);

b) simultaneous ovulation of two or more eggs that matured in the follicles of both ovaries (ovulatio biovarialis);

c) ovulation of several eggs that matured simultaneously within a single follicle (ovulatio unifollicularis).

Twins are the most common type of multiples, with dizygotic (fraternal) twins occurring twice as often as monozygotic (identical) twins. In dizygotic twin pregnancies, the fertilized eggs develop independently, each having its own amniotic and chorionic membranes, as well as a separate vascular network. Examination of the afterbirth reveals two placentas. The dividing membrane between the fetuses in dizygotic twins consists of an amnion-chorion-chorion-amnion Structure, representing a dichorionic diamniotic placentation type. Dizygotic twins may be of different sexes and have either different or identical Blood Groups.

Pregnancy with monozygotic (identical) twins occurs As a result of the fertilization of a multinucleated egg by multiple spermatozoa or the division of the genetic material into two parts during the Cleavage stage, with each part forming an embryo. Monozygotic twins share a single Placenta, decidua, and vascular network, while having either two amnions or one: a monochorionic diamniotic placentation type. Pregnancies with monozygotic twins are more frequently associated with fetal developmental anomalies, velamentous cord insertion, single umbilical artery, and twin-to-twin transfusion syndrome (where blood flows from Arteries to Veins, from one fetus to the other), which can lead to intrauterine growth restriction, cardiovascular failure, anemia, and polyhydramnios in one of the fetuses.

Monozygotic twins are always of the same sex and bear a striking physical resemblance to each other. They share identical blood groups and Rhesus factors. Examination of the afterbirth reveals a single placenta, a dividing membrane between the amniotic cavities consisting solely of two amnions, and a single shared decidua.